Why databases?

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Databases

Why do they exist?

Databases are very important in applications to store and retrieve data in efficient way.

Types

1. Relational databses:

Why do they exist
  • used to store data which is related together.
  • we split and organize this data into tables, and there are relations between these tables as the data is related together.
  • Abides by the ACID rules (Atomicity, Consistency, Isolation, Durability)
more info
  • Widely used
  • They have a structure(schema)
  • schema defines structure, datatypes and limits
  • SQL (Structured Query Language) to query the database
examples
  • postgresql, mysql, oracle
  • coucheDB, when you want to horizontally scale your database

2. Key Value databases

Why do they exist
  • simple, they just store key and value pair efficiently.
  • GET, PUT, DELETE
more info
  • very fast!!!
  • limited by memory, as data increases they suffer
  • often used in caching
  • sometimes used as message queue
examples
  • redis, memcached, etcd

3. Wide column databases

why do they exist
  • if we want a key value store but the value needs to have multiple columns
  • schema less
more info
  • scalable
  • no joins
  • can handle unstructured data. for example, can be used in time series analysis
examples
  • cassandra, hbase

4. Document databases

why do they exist
  • unstructured databses, can be almost used for anything.
  • so if you are starting out without any schema and have no idea what schema might become in future, use this. i.e if data is related together, move away from this
more info
  • documents -> containers for key value pairs
  • collection -> set of documents together
  • unstructured/schemaless, so no schema
  • no joins
  • nested data
  • updates and writes are slow but reads are fast
Examples:
  • mongoDB, dynamoDB, couchDB

Graph databases

why do they exist
  • correletd data
  • relationship between data, ex: users, comments, friends etc.
  • use this if you can visualize the application database structure as graph
examples:
  • Neo4g

Search databases

why do they exist
  • given some data and query, you should be able to search in it(asap)
  • they create a posting list internally to return answers to the queries.
examples:

  • elasticsearch

  • You can always have a combination of different databases😊.